Adding and Subtracting Decimals

Adding and Subtracting Decimals exercise

• Calculate the sum of the decimals.

  Hints

  Line up the two decimals with the decimal points and add together.

  For example,

  For this question we add the right hand column up first. $7 + 8 = 15$ We use the $5$ and carry the tens to the next column, moving left.

  Solution

  The correct answer is $12.5$.

  • Line up the two numbers with the decimal point.
  • Add each column from the right to the left.
  • If any column is greater than $9$ write down the units and carry the tens to the next column on the left.

• Find the sum of the two decimals.

  Hints

  • Line up the numbers with the decimal point
  • If there is a column after the decimal point without a number add in a $0$
  • Start at the right and add up each column

  If the column adds up to a number greater than $9$ we place the units in that column and add the tens to the next column on the left.

  Solution

  The correct answer is $32.42$.

  • Line up the numbers with the decimal point
  • If there is a gap after the decimal point add in a $0$
  • If the column adds up to a number greater than $9$ write the units in the column and add the tens to the next column on the left.

  See steps $1$ to $3$

• Subtract the decimals.

  Hints

  • Line the decimals up with the decimal points as with addition
  • Subtract the bottom number from the top one
  • If the answer to the column would be a negative we use one of the tens from the next column on the left. For example,

  • Start at the right and move left subtracting each column

  For example,

  Solution

  • We cannot do $3 - 6$ so we add a $10$ from the $7$ and do $13 - 6$
  • The next column now becomes $6 - 3$ which is $3$
  • We next do $6 - 5$ then $1 - 0$ to give us $11.37$

• Fencing the chicken pen

  Hints

  Line all three numbers up with the decimal points and add together. See the example here.

  Start with the right column and add each column moving left. See the example here.

  • Add $7 + 6 + 8$
  • As this is $21$ we write down the units, $1$ and carry the tens to the column on the left.
  • Now we add $5 + 2 + 6$ and the extra $2$.
  • As this is $15$ we write down the units, $5$ and carry the tens to the column on the left.
  • Nothing to add the $1$ to there so we can write the $1$.

  Solution

  The answer is $22.2$ metres.

  Start with the right column and add each column moving left.

  • Add $3 + 3 + 6$
  • As this is $12$ we write down the units, $2$ and carry the tens to the column on the left.
  • Now we add $8 + 8 + 5$ and the extra $1$.
  • As this is $22$ we write down the units, $2$ and carry the tens to the column on the left.
  • Nothing to add the $2$ to there so we can write the $2$.

• Find the sum of the decimals.

  Hints

  When adding decimals, line up the numbers with the decimal point. For example,

  Add each column starting at the right and continue left.

  Solution

  The correct answer is $15.76$.

  • Line up the numbers with the decimal point.
  • Add each column starting at the right and continue left.

  See steps $1$ to $4$.

• Determine the amount of flour by addition and subtraction of decimals.

  Hints

  Jack has used $1.4$ kg and $0.75$ kg of the flour.

  We need to add these together first to find the total flour he has used.

  When we have the total of the flour used, we subtract it from the original amount of $2.4$ kg.

  Solution

  The correct answer is $0.25$ kg of flour left.

  • First, add $1.4 + 0.75 = 2.15$
  • Subtract $2.15$ from $2.4$
  • That is $2.4 - 2.15 = 0.25$